1. Field of the Invention
This invention relates to a yarn storage and delivery apparatus and particularly to a yarn storage and delivery apparatus used to feed a yarn under constant tension.
2. Description of the Prior Art
As is known, weaving machines use a yarn storage and delivery apparatus for feeding a weft yarn under constant tension. Such yarn storage and delivery apparatus is used not only for feeding a weft yarn to a weaving machine but also in winders.
There are two types of known yarn storage and delivery apparatuses, the yarn winding drum rotation type or the so-called Savi type and the yarn winding drum stationary type or the so-called Sulzer type. A yarn storage and delivery apparatus of the Savi type keeps the yarn wrapping member stationary while rotatively driving the yarn winding drum to wrap a predetermined amount of yarn therearound for storage. When the weaving machine starts operating, the yarn on the yarn winding drum is unwound therefrom under constant tension to be fed to the weaving machine. Concurrently therewith, the yarn winding drum is rotated to make up for the amount of unwound yarn. That is, while the yarn on the yarn winding drum is being withdrawn, additional yarn is wrapped therearound.
On the other hand, a yarn storage and delivery apparatus of the Sulzer type keeps the yarn winding drum stationary while rotating the yarn wrapping member to wrap a predetermined amount of yarn around the yarn winding drum. As soon as the yarn comes to be unwound, the yarn wrapping member is started to make up for the yarn consumption.
The features and merits and demerits of both types will now be described.
In the Savi type yarn storage and delivery apparatus, since the yarn winding drum is kept rotating all the time, the yarn is caused to balloon even during intermittent delivery of yarn and hence there is little possibility of snarls being formed. Accordingly, the Savi type yarn storage and delivery apparatus is suitable for hard twist yarns. However, if the yarn speed exceeds 800 m/min, the use of a tension ring fitted on the yarn winding drum results in the tension ring finger spreading to decrease the tension until the latter is zero. For this reason, the Savi type has been limited in practical yarn speed to no more than 900 m/min.
On the other hand, in the Sulzer type yarn storage and delivery apparatus, since the yarn winding drum is kept stationary, the yarn hangs down at rest during intermittent delivery of yarn, tending to produce snarls. Thus, this type is not suitable for use with hard twist yarns. The Sulzer type has a feature that there is no variation in tension taking place even when the yarn speed is above 800 m/min, since the tension ring is kept at rest. However, if the yarn speed exceeds 1200 m/min, the yarn wrapping rate becomes so high as to cause yarn breakage which is dangerous. Thus, the Savi type is suitable for use at low yarn speeds of not more than 800 m/min, while the Sulzer type is suitable for use at high yarn speeds of not less than 800 m/min. Both types, however, have the disadvantage of not being applicable to high speed yarn delivery in which the yarn speed exceeds 1200 m/min.